Methods for treating wastewater from exploration for and production of oil and gas

ABSTRACT

Volatile organic compounds (VOCs), such as BTEX methanol and other non-phase separable hydrocarbons may be removed from wastewater obtained from oil or gas exploration or production operations by way of a bioreactor. The bioreactor may employ anaerobic microorganisms that metabolize various VOCs. In some embodiments, such a bioreactor may be configured to treat process flow rates of thousands of barrels of wastewater per hour. Such a bioreactor may comprise a large vessel at a larger water treatment site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/044,973 filed on Oct. 3, 2013, now abandoned and titled “METHODS FORTREATING WASTEWATER FROM EXPLORATION FOR AND PRODUCTION OF OIL AND GAS”which application is a divisional application claiming priority under 35U.S.C. §119(e) to U.S. patent application Ser. No. 13/856,135 filed onApr. 3, 2013, and titled “METHODS, APPARATUSES, SYSTEMS AND FACILITIESFOR TREATING WASTEWATER FROM EXPLORATION FOR AND PRODUCTION OF OIL ANDGAS” which application is a non-provisional application claimingpriority under 35 U.S.C. §119(e) to U.S. patent application Ser. No.61/677,004 filed on Jul. 30, 2012, and titled “METHODS, APPARATUSES,SYSTEMS AND FACILITIES FOR TREATING WASTEWATER FROM EXPLORATION FOR ANDPRODUCTION OF OIL AND GAS,” which applications are expresslyincorporated herein in their entirety by this reference.

TECHNICAL FIELD

This disclosure relates generally to the treatment of wastewaterrecovered from the exploration for and production of oil and gas. Morespecifically, this disclosure relates to apparatuses, systems,facilities and methods for removing non-phase separable organic contentfrom wastewater, including dissolved volatile organic compounds (VOCs),which are widely designated by federal and state regulators as hazardousair pollutants (HAPs).

RELATED ART

Along with oil or gas, water is typically present in oil and gasreservoirs. Thus, when oil and gas are removed from the ground, they areusually accompanied by water. Since the density of water exceeds thedensities of both oil and gas, water is typically located beneath oil orgas within a well. As the well is depleted of its oil or gas, more andmore naturally occurring water accompanies oil or gas out of the well.

In addition, water that has been introduced into a well (i.e., which isnot naturally occurring within an oil and gas reservoir) may also beremoved with oil or gas from the well. Among other purposes, water maybe introduced into a well in a process known as “flooding” to displaceoil or gas within the reservoir. Water may be injected into a well toincrease pressure within the reservoir and to thereby stimulate the wellto maximize its production of oil or gas, a technique that is known inthe art as “hydraulic fracturing.” Like naturally occurring water, waterthat has been introduced into a well accompanies oil or gas out of thewell. “Flow-back water” is water that has been introduced into the welland subsequently removed from the ground along with oil or gas.“Produced water” is naturally occurring ground water that has beenremoved from a well.

Regardless of its origin, any water that is removed from an oil or gaswell is considered to be an exploration and production (E&P) waste.Specifically, E&P wastewater can include a number of hazardous airpollutants (HAPs), including volatile organic compounds (VOCs), such asthe so-called “BTEX” materials; i.e., benzene, toluene, ethylbenzene andxylene. In addition, in colder environments, methanol (CH3OH), anotherHAP, may be used as an antifreeze in water introduced into a well and,thus, be present in water removed from the well.

Despite the presence of HAPs, E&P wastewater has conventionally beentransported to water treatment, or remediation, facilities, where phase(i.e., hydrocarbons immiscible in water) separable hydrocarbons andsludge (i.e., hydrocarbon coated or impregnated solids) may be removedfrom the E&P wastewater before disposing of it. One of the morecost-efficient methods for disposing of E&P wastewater employsevaporation ponds. From an evaporation pond, the E&P wastewater may beintroduced back into the environment (e.g., into the atmosphere as watervapor; less desirably, through the ground; etc.), along with a portionof the vaporized HAPs that exited the well with the water. From anenvironmental perspective, the placement of E&P wastewater that includesdissolved HAPs into evaporation ponds is less desirable than other, moreexpensive disposal methods.

The Environmental Protection Agency (EPA) and analogous agencies ofvarious states have implemented environmental regulations requiring thatE&P wastewater be treated before it may be placed into evaporationponds. The most stringent regulations mandate that E&P wastewater be“treated by passing the E&P wastewater through various filters, enhancedgravity separation, emulsification removers, chemical treatment andother advanced treatment devices. Such processes produce gasoline anddiesel range hydrocarbons, waxes, heavy oils and oil-coated andimpregnated sediment waste that are reclaimed, burned, land farmed orlandfilled. Although advanced physical treatment devices are able topolish phase separable VOCs from E&P wastewater, they do not capturesoluble VOCs, some of which are HAPs, nor will they capture otherorganic components from the E&P wastewater. Thus, even when advancedphysical treatment techniques are used to treat E&P wastewater,significant amounts of dissolved VOCs remain in the treated water whenit is introduced into an evaporation pond, potentially polluting theatmosphere and ground and surface water.

SUMMARY

This disclosure relates to the treatment of exploration and production(E&P) wastewater, which is also more simply referred to herein as“wastewater,” recovered from oil and gas exploration and productionsites. In addition to being useful for treating E&P wastewater, theapparatuses, systems and methods disclosed herein may be used to treatwastewater from other sources. More specifically, apparatuses, systems,facilities and methods for removing dissolved volatile organic compounds(VOCs), which are widely considered to be hazardous air pollutants(HAPs), from wastewater. The various VOCs that may be removed fromwastewater include, but are not limited to, methanol (i.e., methylalcohol) and the so-called “BTEX” materials; i.e., benzene, toluene,ethylbenzene and xylene. These materials may be safely removed fromwastewater and converted by anaerobic bacteria to less harmfulsubstances (e.g., carbon dioxide (CO2) and water vapor) and methane(CH4), which is natural gas and can be reclaimed and used for the samepurposes as natural gas.

In one aspect, a bioreactor, or digester, for treating wastewater mayinclude an anaerobic vessel or partition that provides a favorableenvironment for anaerobic microorganisms. In addition, the bioreactormay include one or more elements for mixing (continuously, periodically,etc.) the contents of the anaerobic vessel, including the anaerobicmicroorganisms and any wastewater within the anaerobic vessel.

The anaerobic vessel of a bioreactor may take a variety ofconfigurations, depending at least in part upon the flow rate ofwastewater to be treated and the location where the wastewater is to betreated. Where relatively small volumes of wastewater are to be treated(e.g., on the order of hundreds of barrels, 500 barrels or less per day)the anaerobic vessel may comprise a tank, such as a frac tank of thetype commonly used in the oil and gas industry. When larger volumes ofwastewater are to be treated, the anaerobic vessel of the bioreactor maycomprise a pool, pond or other vessel constructed for this purpose at awastewater treatment facility.

The anaerobic microorganisms of a bioreactor may be selected tometabolize, or digest, various VOCs that have dissolved in thewastewater, including methanol and BTEX materials, while withstandingthe harsh conditions that are typically present in wastewater from oiland gas exploration or production (e.g., the VOCs, extreme temperatures,high salinity, sediment, metals and the like.). The ability of theanaerobic microorganisms to metabolize VOCs may be optimized andmaintained by carefully monitoring and controlling various conditionswithin the anaerobic vessel of the bioreactor.

In another aspect, this disclosure relates to systems for treating E&Pwastewater, which are also referred to herein as “wastewater treatmentsystems.” In addition to a bioreactor, such a wastewater treatmentsystem may include a variety of other elements, such as: components forisolating the wastewater from light non-aqueous phase liquids (LNAPLs)(e.g., hydrocarbons, etc.), dense non-aqueous phase liquids (DNAPLs)(e.g., crude oil having API gravity of 10 or less) and solid materials(i.e., sludge); components for recovering hydrocarbons (e.g., oil, gas,etc.) and other LNAPLs from wastewater; and components beforereintroducing treated wastewater to the environment (e.g., byevaporation, etc.). In addition, a system for treating wastewater mayinclude one or more components for facilitating the removal ofundissolved VOCs from wastewater and eliminating the undissolved VOCsthat have been removed, as well as one or more components for filteringany remaining VOCs from treated wastewater.

On a large scale, such a system may be incorporated into a wastewatertreatment facility or wastewater treatment site. In the context of awastewater treatment site, an oil-water separator (OWS), may provide forsome initial separation of wastewater from hydrocarbons and sludge.Separation of the wastewater from hydrocarbons and/or sludge may also beachieved in a surge or stilling basin, which may be configured tocollect and store a large volume of wastewater until the wastewater canbe treated or further processed. In addition to the OWS and stillingbasin, a wastewater treatment site may include a bioreactor vessel. Insome embodiments, a wastewater treatment site may include one or moremethods and types of equipment to reintroduce treated wastewater to theenvironment. Of course, a wastewater treatment site may also includeother elements (e.g., one or more hydrocarbon removal components, flaresor incinerators, filters, etc.) that facilitate the removal of VOCs fromwastewater, as well as the recovery of hydrocarbons. Each successivecomponent, or location, within the wastewater treatment site may belocated at a lower elevation than the previous element, or location,exploiting the force of gravity to move wastewater from one location tothe next.

Methods for treating wastewater are also disclosed. Broadly, suchmethods include isolating wastewater from phase separable hydrocarbonsand solid materials (i.e., sludge) and removing VOCs from thewastewater. Hydrocarbons dissolved in wastewater may be metabolized byanaerobic bacteria to remove them from wastewater.

In a specific embodiment of a method for treating wastewater, thewastewater may be transported to a wastewater treatment site. An initialseparation of the wastewater from hydrocarbons and solids may beeffected by introducing the wastewater to an OWS. The hydrocarbons maybe recovered, the solids may be disposed of and the wastewater issubjected to further treatment. Further separation of hydrocarbons andsolids from the yet-to-be treated wastewater, or untreated wastewater,may be achieved by introducing the wastewater into a stilling basin. Thedesired level of separation may be accomplished in a stilling basin.Partially treated wastewater may be released from the stilling basininto a bioreactor vessel. In a bioreactor, various types of anaerobicmicro-organisms metabolize dissolved VOCs. Metabolites includesubstances less toxic to human health such as methane. Following removalof dissolved VOCs (e.g., when the levels of dissolved VOCs in thetreated wastewater reach acceptable levels, etc.), the treatedwastewater may be released from the bioreactor.

During one or more of the foregoing processes, volatilized hydrocarbonsmay be removed from the wastewater and flared, or incinerated.

The treated wastewater may be filtered or directed to an evaporationpond, where it may be introduced, by evaporation, back into theenvironment.

Other aspects, as well as features and advantages of various aspects, ofthe disclosed subject matter will become apparent to those of ordinaryskill in the art through consideration of the ensuing description, theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 schematically illustrates an embodiment of a bioreactor forremoving VOCs from wastewater;

FIG. 2 is a plan view of an embodiment of a large-scale bioreactor thatmay be included in a wastewater treatment site;

FIG. 3 is a cross-sectional representation of the embodiment of thebioreactor shown in FIG. 2;

FIG. 4 depicts an embodiment of a wastewater treatment site thatincludes a bioreactor of the type shown in FIGS. 2 and 3; and

FIG. 5 is a schematic representation of a wastewater treatment site, ofwhich the wastewater treatment site of FIG. 4 is an embodiment.

DETAILED DESCRIPTION

According to one aspect of this disclosure, a properly configuredbioreactor may be configured to remove VOCs dissolved in wastewater fromthe wastewater, such as E&P wastewater. In various embodiments, abioreactor may include an anaerobic vessel for the wastewater, as wellas anaerobic microorganisms (e.g., anaerobic bacteria) that willmetabolize the organic compounds in wastewater, including, but notlimited to, VOCs. In some embodiments, the bioreactor may also include amixing system for distributing the anaerobic microorganisms throughoutthe wastewater within the anaerobic vessel. A bioreactor may alsoinclude an outlet, from which gases that are produced by the anaerobicmicroorganisms as they metabolize dissolved VOCs may be collected.

As shown in FIG. 1, a bioreactor 10 may include a selectively sealedtank 12, which is also referred to hereinafter as a “tank” for the sakeof simplicity. The tank 12 includes an interior 14 and an exterior 16,as well as an inlet 18 to the interior 14 of the tank 12 and outlets 20and 22 to the exterior 16 of the tank 12. In addition to the tank 12,the bioreactor includes wastewater 24 within the interior 14 of the tank12 and a blend of anaerobic microorganisms 26 in the wastewater 24. Asolids (sludge) collection system 28 may communicate with the bottom ofthe interior 14 of the tank 12. A mixing system 30 associated with thetank 12 may distribute the anaerobic microorganisms 26 throughout thewastewater 24 within the interior 14 of the tank 12.

The tank 12 may have a size conducive to the flow rate of wastewater 24to be treated by the bioreactor 10. Without limitation, a tank 12 mayhave a volume on the order of a hundred barrels to a thousand barrels.In a specific embodiment, a so-called “frac tank,” of a type commonlyused in the oil and gas industry may be used to form the tank 12. When afrac tank is used as the tank 12 of a bioreactor 10, it may have acapacity of about 400 barrels.

Wastewater 24 is introduced into the interior 14 of the tank 12 throughthe inlet 18 of the tank 12. The outlets 20 and 22 enable removal ofsubstances from the interior 14 of the tank 12 and their communicationto locations outside of the tank 12's exterior 16. As illustrated, oneof the outlets (i.e., outlet 20 in the illustrated embodiment) may belocated near a top of the tank 12 so as to enable clarification of thewastewater 24 (e.g., by gravity, etc.) as the wastewater 24 is removedfrom the tank 12 (e.g., the wastewater 24, etc.), leaving sludge and theanaerobic microorganisms 26 within the interior 14 of the tank 12. Inthe illustrated embodiment, a vertically oriented baffle 21 creates aphysical barrier between the majority of the interior 14 of the tank 12and the outlet 20 to enable clarification of wastewater 24 exiting theinterior 14 of the tank 12. The other outlet 22 may also be located neara top of the tank 12 to enable the removal of gases (e.g., methane,etc.) produced during the treatment of the wastewater 24 (e.g., themetabolism of VOCs by the anaerobic microorganisms 26, etc.) from theinterior 14 of the tank 12, enabling pressure that builds within theinterior 14 of the tank 12 to be periodically or continuously releasedand collected. Of course, a valve may be associated with each of theinlet 18 and the outlets 20 and 22 to control the movement of fluidsinto or out of the tank 12.

The mixing system 30 may be configured to move the wastewater 24, alongwith the VOCs and anaerobic microorganisms 26 therein, with lowhydraulic shear. In the depicted embodiment, the mixing system 30includes a low shear pump 32 that draws wastewater 24 into an inlet of aconduit 34 at a first location 141 within the interior 14 of the tank 12and causes the wastewater 24 to flow into one or more elongated, tubularbaffles 36. Each tubular baffle 36 extends along the length of theinterior 14 of the tank 12, and may be located anywhere within the tank,including at or near the center of the interior 14 of the tank 12. Eachtubular baffle 36 includes a series of holes 38 spaced at variouslocations along its length. The holes 38 may be fitted with nozzles andmay be positioned and oriented to cause the wastewater 24 to flow in adesired manner.

The anaerobic microorganisms 26 within the interior 14 of the tank 12may comprise one or more different microorganisms (e.g., bacteria, etc.)that metabolize the various VOCs (e.g., BTEX materials, methanol, etc.).Since the VOCs are constantly contained to prevent their introductioninto the environment and, little or no elemental oxygen (O2) is presentin or at the surface of the wastewater 24, the microorganisms whichmetabolize the VOCs are able to live with little or no free oxygen;i.e., they are anaerobic. As different microorganisms may metabolize oneor more types of VOCs, but not all of the different types of VOCs thatare typically present in wastewater 24, the anaerobic microorganisms 26that are used in the bioreactor 10 may include a mixture of differentmicroorganisms. In a specific embodiment, the anaerobic microorganisms26 comprise a mixture of microorganisms from wastewater treatment plantswith sludge having a high total dissolved solids (TDS) content (e.g., aTDS content of about 1,500 mg/L or more, a TDS content of about 2,500mg/L, etc.). In some embodiments, the anaerobic microorganisms may beacclimated to withstand a TDS content of up to about 20,000 mg/L, up toabout 25,000 mg/L, or more.

In a specific embodiment, the anaerobic microorganisms 26 may include ablend of acid formers and methane formers. The acid formers, which maybe facultative anaerobes (i.e., rugged microorganisms that can survivein both aerobic environments (by respiration) and anaerobic environments(by fermentation)), metabolize organic materials (e.g., VOCs, etc.) byhydrolysis, then ferment the hydrolyzed materials to form acids andalcohols. The methane formers, which are obligate anaerobes (i.e.,microorganisms that can only survive in anaerobic environments),metabolize the acids and alcohols generated by the acid formers and anymethanol present in the wastewater 24, as well as hydrogen (H2) andcarbon dioxide (CO2), to methane (CH3).

In some embodiments, because wastewater 24 sometimes has a high TDScontent, (or high salinity), the anaerobic microorganisms 26 may also beselected for their ability to survive or thrive in saline conditions.Microorganisms that can live in saltwater are often referred to as“halotolerant” and include halophilic (i.e., salt loving)microorganisms, which thrive in saltwater.

Because of its size, the bioreactor 10 shown in FIG. 1 may be relativelyportable (e.g., be transported on a trailer; comprise part of a tanker,such as a tanker trailer or tanker truck; etc.). The portability of abioreactor 10 may enable wastewater 24 or other wastewater that includesdissolved VOCs to be treated at or near the site from which such wateris obtained.

Turning now to FIGS. 2 and 3, an embodiment of a much larger scalebioreactor 110 is depicted. Like the smaller version shown in FIG. 1,the bioreactor 110 includes a vessel 112 with an interior 114, an inlet118, and outlets 120 and 122. The bioreactor 110 also includes anaerobicmicroorganisms 126 for treating water 124 within the interior 114 of thevessel 112. In addition, the bioreactor 110 may include one or moresludge management systems 128 (not shown) that communicate with thebottom of the vessel 112's interior 114, a mixing system 130 and a leakdetection system 140.

Because the bioreactor 110 is large, its vessel 112 is also large. Invarious embodiments, the vessel 112 of a large bioreactor may comprise apool or, as depicted, a pond 150. A pond 150, which may comprise arecessed area formed in the ground, may be constructed to have anydesired capacity. Without limitation, the pond 150 may have a capacityof 1,000 barrels or more. In some embodiments, the volume of the pond150 may be 10,000 barrels or more, or even 50,000 barrels or more (e.g.,55,000 barrels). While various configurations of ponds 150 are withinthe scope of this disclosure, relatively shallow ponds 150 withrelatively large surface areas are desirable, as larger surface areassupport more of the anaerobic microorganisms 126 of the bioreactor 110.

In embodiments where the pond 150 comprises a recessed area formed inthe ground G, a base 152 of the pond 150 may comprise up to twelveinches or more of low-permeability compacted soil. The soil may becompacted to at least 95% of its maximum dry density of as measured byASTM D-698, and have a permeability as measured by a hydraulicconductivity of 1×10⁻⁷ cm/sec or less. A cushion 154 of compacted sandor material having similar hydraulic tranmissivity may sit atop the base152 of the pond 150. An outer periphery of the pond 150 may be definedby an embankment 156, or a berm or a leading, that is raised somewhatrelative to the surface of the ground G within which the pond 150 isformed. The embankment 156 may have an interior slope 158 into theinterior 114 of the vessel 112 and, thus, of the pond 150, as well as anexterior slope 160 from a crest 162 at the top of the embankment 156 tothe surface of the ground G adjacent to the pond 150. In a specificembodiment, the crest 162 may have a width of about 12 feet or more,while the interior slope 158 may be about one foot vertical for everytwo feet horizontal (1:2) or shallower and the exterior slope 160 may beabout one foot vertical for every two feet horizontal (1:2) orshallower. In a specific but non-limiting embodiment, the pond 150 maybe rectangular in shape, with a length of about 400 feet, a width ofabout 100 feet and a depth of about 20 feet.

The pond 150 may also include an anchoring trench 164 within the crest162 of the embankment 156. The anchoring trench 164 may be configured toreceive anchors 165 for other components of the vessel 112 of thebioreactor 110, as will be described in further detail hereinafter.

In addition to the pond 150, the vessel 112 of the bioreactor 110 mayinclude one or more liners 168 on the base 152 of the pond 150 and onthe interior slope 158 of the pond 150's embankment 156. The liner(s)168 provide(s) a barrier that prevents dissolved VOCs and otherpotential pollutants in water 124 (e.g., flow-back water, producedwater, other E&P wastewater, etc.) within the pond 150 (i.e., within theinterior 114 of the vessel 112) from seeping into the ground G. In aspecific embodiment, the vessel 112 may include a pair of superimposedsheets of high density polyethylene (HDPE) having a thickness of 60 mils(0.060 inch, or about 1.5 mm). Each liner 168 may be anchored atlocations adjacent to its outer periphery. As a non-limiting example,the liners 168 may be anchored within the anchoring trench 164 in thecrest 162 of the embankment 156 with suitable anchors 165, such ascompacted clay. Further anchoring may be provided by way of a concretecurb 166 disposed over earthen or plastic liners 168 (e.g., constructeddirectly on top of earthen or plastic liners 168).

The vessel 112 also includes a cover 170, which prevents VOCs in thewater 124 in the pond 150 and, thus, within the interior 114 of thevessel 112 from escaping to the atmosphere. The cover 170 may comprise aflexible material, and may be configured to remain in place against thesurfaces of the pond 150 and of any water 124 therein as the level ofthe surface of the water 124 within the pond 150 changes. In embodimentswhere the cover 170 is flexible, it may accommodate any gases and/orvapors that build up within the bioreactor 110, providing temporarystorage for such gases and/or vapors until they can be removed from thebioreactor 110 and treated (e.g., incinerated, burned as fuel, etc.).

In a specific, but non-limiting embodiment, the cover 170 may comprise40 mil thick fiber reinforced HDPE. Outer peripheral portions of thecover 170 may be anchored in place by securing a brace 167 (e.g., withbolts, etc.) over the outer peripheral portions of the cover 170, whichare positioned on an outer periphery of the curb 166, to the curb 166.In addition, restraints, such as cables, may be positioned over andextend across one or more locations of the cover 170 to ensure that itremains free from excessive aeolian flutter during high wind events.

The inlet 118 of the vessel 112 is configured to introduce untreatedwastewater 124U into the interior 114 of the vessel 112. Theconfiguration of the inlet 118 of the bioreactor 110 may depend, atleast in part, on the source of the untreated wastewater 124U that is tobe introduced into the vessel 112. In embodiments where untreatedwastewater 124U is to be introduced into the vessel 112 from a tanker,the inlet 118 may simply comprise an opening into which a hose from thetanker may be introduced or a fitting to which a hose from the tankermay be coupled. In embodiments where the untreated wastewater 124U istransported from another component of a system or site where thebioreactor 110 is located, the inlet 118 may comprise a channel or aconduit that enables the untreated wastewater 124U to flow from anupstream location to the vessel 112.

Outlet 120 of the vessel 112 enables treated wastewater 124T to beremoved from the interior 114 of the vessel 112. The configuration ofthe outlet 120 depends, at least partially, upon the intendeddestination of the treated wastewater 124T. The outlet 120 may comprisea channel or a conduit that enables the treated wastewater 124T to flowto a location downstream from the vessel 112. In some embodiments, theoutlet 120 may comprise a conduit that extends from a location at ornear the base 152 of the pond 150 to a location at or near the top ofthe pond 150. A pump may enable water to be removed from the vessel 112through such an embodiment of outlet 120. In such embodiments, theconfiguration and/or orientation of the outlet 120 may clarify water asit is removed from the vessel 112.

Gases generated within the vessel 112, including products of themetabolism of VOCs (e.g., CO2, H2O, methane, etc.), may be collectedthrough one or more gas outlets 122 of the vessel 112. Each gas outlet122 may communicate with or comprise a conduit that vents gasses fromthe interior 114 of the vessel 112 and, in some embodiments, transportsthe gases to one or more locations where they may be collected and/orprocessed.

It may be desirable to maintain a periodic or continuous flow of liquidswithin the interior 114 of the vessel 112. Accordingly, a mixing system130 may be associated with the interior 114 of the vessel 112. As willbe appreciated by those of ordinary skill in the art, a variety ofdifferent types of mixing systems 130 may be employed; FIG. 2 depictsonly one embodiment of many possibilities. The depicted mixing system130 includes at least one conduit 132 with an inlet 134 and one or morebaffles 136 (one is shown in the depicted embodiment). Each baffle 136includes a plurality of outlets 137 (e.g., openings, openings that havebeen fitted with nozzles, etc.). The depicted mixing system 130 alsoincludes a pump 138, which communicates with the conduit 132 at alocation along the length of the conduit 132, between its inlet 134 andeach baffle 136. The pump 138 is located and configured to draw fluidsfrom the interior 114 of the vessel 112 and into the inlet 134 of theconduit 132, then force the fluids into each baffle 136 and out of itsoutlets 137, back into the interior 114 of the vessel 112. Variousparameters, such as the amount of pressure generated by the pump 138,the location of each baffle 136, the orientations of the outlets 137 andthe pressure generated by the outlets 137, may dictate the manner inwhich fluids move through (e.g., are circulated within, etc.) theinterior 114 of the vessel 112. Such movement may homogenize thecontents of the water 124 within the interior 114 and facilitate (e.g.,increase the rate of, etc.) removal of VOCs from the water 124.Mechanical mixers may also be installed to augment or replace hydraulicmixing described herein.

In addition to the vessel 112, a bioreactor 110 may include a leakdetection system 140. A leak detection system 140 may be associated withthe vessel 112 in such a way that any leakage by the vessel 112 may bedetected, as may a rate of leakage. In the embodiment illustrated byFIG. 3, the leak detection system 140 may include a plurality ofdetection pipes 142 that communicate with a collection pipe 144 (FIG.2). The collection pipe 144, in turn, communicates with a verticallyoriented observation well 146 located outside of the bioreactor 110'svessel 112 or an observation well located inside the vessel.

More specifically, the detection pipes 142 may comprise perforated orwater permeable conduits. Each detection pipe 142 may be located at thebase 152 of the vessel 112 so that any water that leaks through theprimary (plastic sheet) liner 168 may be detected and removed at such arate as to limit the hydraulic pressure applied to the secondary(lowest) liner(s) 168. In the depicted embodiment, each detection pipe142 is located at the base 152 of the pond 150, between the layers ofthe liner 168. In some embodiments, the detection pipe(s) 142, alongwith underlying portions of a liner 168, may be recessed withincompacted clay at the base of the pond 150 and optionally surrounded bya course material (e.g., pea gravel, etc.) and/or covered with a waterpermeable filter cloth. In a specific embodiment, each detection pipe142 may comprise a four inch diameter. Each detection pipe 142 may beoriented substantially parallel to other, equally spaced detection pipes142 (e.g., at 50 foot centers relative to one another, etc.), andoriented at an appropriate slope to the collection pipe 144, such thatany water that flows into a detection pipe 142 will flow downhill to thecollection pipe 144 and the time of travel will be sufficient to allowrapid detection of liner failure. The collection pipe 144, or varioussections thereof, are also oriented at slight downward angles toward abottom end 147 of the observation well 146. From the observation well146, any leakage of water 124 from the interior 114 of the vessel 112may be detected. Changes in the level of water within the observationwell 146 may also be used to provide an indication of the rate at whichwater is leaking from the interior 114 of the vessel 112.

The anaerobic microorganisms 126 of the bioreactor 110 may havecharacteristics that are the same as or similar to the anaerobicmicroorganisms 26 of the bioreactor 10 described in reference to FIG. 1.For example, the anaerobic microorganisms 126 may reduce or eliminatedissolved VOCs, such as methanol and BTEX in E&P wastewater.

With reference now directed to FIGS. 4 and 5, an embodiment of a systemfor treating, or remediating wastewater, such as wastewater obtainedduring oil or gas exploration or production operations, is illustrated.In particular, FIG. 4 illustrates a water treatment site 200 configuredfor the large scale treatment of wastewater.

The water treatment site 200 includes a large-scale bioreactor 110, aswell as a variety of other components. The various components of thewater treatment site 200 are configured to collect large amounts ofwater (e.g., wastewater, etc.) on a substantially continuous basis. Asan example, a water treatment site 200 may be configured to receive andprocess up to four thousand barrels of wastewater each day.

In some embodiments, the water treatment site 200 may include one ormore components that are configured to enable various phases (e.g.,LNAPLs, water, sludge, etc.) to separate from one another, a bioreactor(e.g., bioreactor 110, an embodiment of which is depicted by FIGS. 2 and3, etc.) and, optionally, one or more downstream treatment elements,such as a filter, a clarifier, one or more evaporation ponds, or thelike.

Among the various components of the embodiment of water treatment site200 shown in FIGS. 4 and 5 are one or more oil water separators (OWS)220, one or more storage tanks 230, a flare 240 or incinerator, astilling basin 250, one or more bioreactors 110, a filter 290 and one ormore evaporation ponds 300.

The OWS 220 may comprise an in-ground tank that is configured to receiveup to four thousand barrels of E&P wastewater daily and hold severalthousand or more, barrels of liquid. As wastewater is typicallyaccompanied by residual hydrocarbons and sludge including, but notlimited to gasoline and diesel range organics, heavy oils, waxes andsludge, the OWS 220 may be the first component of the water treatmentsite 200 where wastewater is processed. Specifically, the OWS 220 may beconfigured to receive wastewater and to hold the wastewater for asufficient period of time to enable the LNAPLs, water and sludge toseparate.

Wastewater, such as E&P wastewater may be delivered to the watertreatment site 200 and to the OWS 220 by tankers 205. Accordingly, theOWS 220 may be positioned at a location of the water treatment site 200accessible to large trucks and tractor-trailers. In addition, in orderto facilitate the flow of wastewater through the water treatment site200, the OWS 220 may be positioned at a higher elevation than other,downstream components of the water treatment site 200. The OWS 220comprises a vessel configured to facilitate an initial, rough separationof various phases (i.e., LNAPLs, water, sludge, etc.) from thewastewater. In some embodiments, the OWS 220 may be configured to remainsealed or substantially sealed from the environment (e.g., to preventthe release of VOCs into the atmosphere, etc.) as various phases of thewastewater separate from one another. The OWS 220 may operate under avacuum (e.g., not greater than ten inches of water).

A hydrocarbon recovery unit 225 may be configured for use with each OWS220 to remove hydrocarbons and other LNAPLs from within the OWS 220. Ina specific embodiment, the hydrocarbon recovery unit 225 may comprise alow-shear pump (e.g., a peristaltic pump, an air-operated diaphragmpump, a gear pump, etc.) and a conduit. The pump may be associated withthe conduit in a manner that, while gradually lowering the conduit intothe LNAPLs and other hydrocarbons near the top of the contents of theOWS 220, enables LNAPLs to be drawn from the OWS 220 and transported toa storage tank 230. The conduit may be configured (e.g., with atransparent region, etc.) to enable viewing of the contents of theconduit; for example, to enable a determination of whether LNAPLs orwater are flowing through the conduit as the conduit is lowered into theOWS 220. In another specific embodiment, the hydrocarbon recovery unit225 may comprise an auto-skimmer of known type. A conduit of ahydrocarbon recovery unit 225 may direct the LNAPLs into a tanker 205.Alternatively, the conduit of such an embodiment of hydrocarbon recoveryunit 225 may transport the LNAPLs to a storage tank 230.

Limited, one-directional gas and/or vapor communication between each OWS220 and the flare 240 may be established by way of a conduit 227 betweenthe OWS 220 and the flare 240 equipped with check valves or detonationarrestors.

A flare 240, or incinerator, and its associated fuel source (e.g., atank of propane, etc.) may be present at a water treatment site 200 toreceive gas and/or vapors from one or more other components of the watertreatment site 200. By way of example, the flare 240 may receive gasand/or vapors from one or more of the OWS 220, the stilling basin 250and bioreactor 110. As the flare 240 receives gases and/or vapors, suchas any VOCs, it may incinerate those gases or vapors to form lessharmful byproducts that may then be released into the atmosphere. Theflare 240 may have any suitable configuration known in the art.

One or more conduits 242, or “vapor lines,” may communicate gases and/orvapors from one or more other components of the water treatment site 200to the flare 240. The gases and/or vapors may be drawn into and througheach conduit 242 to the flare 240 by way of a negative pressure source244. In a specific but non-limiting embodiment, the negative pressuresource 244 may comprise a regenerative blower, which may draw a vacuumof about five inches of water, and may draw a vacuum of up to about 60inches of water.

In addition to drawing gases and/or vapors off of one or more componentsof the water treatment site 200, the negative pressure source 244 mayapply a vacuum to those components. When the negative pressure source244 communicates with the stilling basin 250 and/or the bioreactor 110,any vacuum applied to either of those components may draw the cover (notshown for the stilling basin 250, cover 170 of the bioreactor 110) ofthat component onto the surface of its contents (e.g., the wastewatertherein, etc.), which may provide a substantially anaerobic environmentor a totally anaerobic environment within the stilling basin 250 and thebioreactor 110, and may prevent billowing of the cover(s) 170.

Wastewater may be communicated from the OWS 220 to downstream componentsof the water treatment site 200 by way of a conduit 246 and, optionally,one or more valves. In the embodiment of water treatment site 200illustrated by FIG. 4, the conduit 246 may extend to the stilling basin250.

At the stilling basin 250, further separation of residual LNAPLs (e.g.,hydrocarbons, etc.) and sludge (e.g., DNAPLs, solids, etc.) from thewater may be achieved. The volume of the stilling basin 250 issignificantly larger than the volume of the OWS 220. Thus the water mayreside in the stilling basin 250 for a much longer period of time thanit may reside within the OWS 220 without disrupting the rate at whichwastewater may be delivered to and treated by the water treatment site200. Accordingly, the stilling basin 250 may also be referred to as a“surge pond.” The stilling basin 250 may, in some embodiments, have acapacity of 10,000 barrels or more (e.g., 50,000 barrels, 80,000barrels, 100,000 barrels, etc.). In order to prevent any VOCs that aredissolved in the water from escaping into the environment, the stillingbasin 250 may be configured in a manner similar to the vessel 112 of thebioreactor 110 shown in FIGS. 2 and 3. For example, the stilling basin250 may be surrounded by an embankment, the base of the pond and aninterior slope of the embankment may be covered with a liner, and acover may be disposed over the contents of the stilling basin (whichcover may be configured similar to and function in a similar manner tothe cover 170 of the bioreactor 110). In addition, the stilling basin250 may include a leak detection system similar to the leak detectionsystem 140 shown in FIG. 2.

Since the primary purpose of the stilling basin 250 is to enable furtherseparation of LNAPLs, such as hydrocarbons, and sludge from thewastewater, hydrocarbon and sludge collection systems may also beassociated with the stilling basin 250. LNAPLs may be removed from thestilling basin 250 in any suitable manner. As an example, anauto-skimmer of known type may be used to remove LNAPLs from the surfaceof the wastewater. In another example, as described below, LNAPLs may beseparated from wastewater at an outlet of the stilling basin 250.

Any LNAPLs collected from the stilling basin 250 may be placed in acollection tank and, ultimately, transported to a storage tank 230,where the LNAPLs will be stored until sufficient volumes are collectedto justify their transportation from the water treatment site 200 to arefinery.

Water may be removed from (e.g., flow out of, be pumped out of, etc.)the stilling basin 250 through an outlet 258 of the stilling basin 250.In the depicted embodiment, one or more valves 260, 261, 262, 263 maycontrol the flow of water out of the stilling basin 250 to locationsdownstream from the stilling basin. When valve 260 is closed, no watermay flow from the outlet 258 of the stilling basin 250. Conversely, whenthe valve 260 is open, water may flow through the outlet 258 and, thus,out of the stilling basin 250.

Further, in embodiments where two or more valves 260, 261, 262 and 263are associated with the outlet 258 of the stilling basin 250, the valves260, 261, 262 and 263 may be selectively operated in a manner thatcontrols the destination of the water as it flows from the outlet 258 ofthe stilling basin 250. For example, when valves 260 and 263 are openand valve(s) 261, 262 is (are) closed, water may flow from the outlet258 of the stilling basin 250 to the inlet 118 of the vessel 112 of thebioreactor 110. In embodiments where the bioreactor 110 is located at alower elevation than the stilling basin 250, the water may flow underforce of gravity. Alternatively, when valve 260 and valve 261 are openand valve(s) 262, 263 is (are) closed, water may flow into a bypasssystem 270, which bypasses the bioreactor 110, and may also enable thewater to flow downstream to another component (e.g., a filter 290, aclarifier 294, etc.) of the water treatment site 200. The bypass system270 may be configured to enable the communication of water directly fromthe stilling basin 250 to a filter 290.

As another alternative, when valves 260 and 262 are open and valve(s)261, 263 is (are) closed, LNAPLs and possibly water may flow to anotherdownstream component of the water treatment site 200, such as a holdingtank 296. When the valves 260-263 are oriented with valves 260 and 262open and valve(s) 261, 263 closed, and in embodiments where the outlet258 from the stilling basin 250 comprises a conduit with an upper limitat a known elevation, the valves 260-263 and the outlet 258 may be usedtogether to remove LNAPLs from the surface of wastewater within thestilling basin 250. More specifically, wastewater may be removed fromthe stilling basin 250 until an upper surface of the wastewater is levelwith the upper limit of the outlet 258. Depending upon the orientationsof valves 261 and 263, the wastewater may be directed into thebioreactor 110 or allowed to bypass the bioreactor 110. Once theinterface between the wastewater and any LNAPLs on the surface of thewastewater (i.e., the upper surface of the wastewater and, thus, thelower surface of any LNAPLs on the surface of the wastewater) is at thesame elevation as, or level with, the upper limit of the outlet 258, theorientations of valves 262 and 261, 263 may be switched (e.g., valve261, 263 may be closed and valve 262 may be opened), directing theLNAPLs that flow through the outlet 258 to a location other than thebioreactor 110 or any other downstream destination for the wastewater.In a specific embodiment, the LNAPLs may be directed into a collectiontank 265, where any water that accompanied the LNAPLs out of thestilling basin 250 may be allowed to separate from the LNAPLs. TheLNAPLs may be taken to a storage tank 230. The water may be reintroducedinto the stilling basin 250, introduced into the bioreactor 110 ortransported to another downstream treatment component of the watertreatment site 200.

As disclosed previously herein, the filter 290 may receive wastewaterfrom the bypass system 270. The filter 290 may also be positioned andconfigured to receive water from the outlet 120 of the bioreactor 110;the flow of water from the outlet 120 of the bioreactor 110 may becontrolled by a valve 280.

The filter 290 may be configured to remove at least some VOCs, from thewater. Without limitation, the filter 290 may comprise a walnut shellfilter of a known type. However the filter may be selected for removalof known VOCs, not effectively removed by the bioreactor 110.

Alternatively, the water treatment site 200 may be configured to enablewater that flows from the bioreactor 110 to bypass the filter 290.

In addition to the filter 290, or as an alternative, the water treatmentsite 200 may include a clarifier 294. The clarifier 294, which may beconfigured in any suitable manner known in the art, may be locateddownstream from the bioreactor 110 and configured to remove sludge fromwater that has been treated by the bioreactor 110.

Water from the filter 290 and/or the clarifier 294 may be introducedinto a break tank 298, which may be configured to load the treated waterinto a tanker 205. Alternatively, the treated water may be introducedinto one or more other treatment components (e.g., another filter, areverse osmosis (RO) system, an evaporation pond 300, etc.), which maybe located downstream from the bioreactor 110, the filter 290 and/or theclarifier 294. In the embodiment of water treatment site 200 illustratedby FIG. 4, water from the bioreactor 110 and/or the filter 290 may flowinto one or more evaporation ponds 300. Each evaporation pond 300 may belocated at a lower elevation than the bioreactor 110 and/or the filter290, and may be configured in a manner known in the art. In embodimentswhere a water treatment site 200 includes a plurality of evaporationponds 300 arranged in series with one another, each successiveevaporation pond 300 may be located at a lower elevation than thepreceding evaporation pond 300. In order, upstream to downstream, theLNAPL content in water decreases from one evaporation pond 300 to thenext, while the content of TDSs, including salt, in the water increasesfrom one evaporation pond 300 to the next. More specifically, eachevaporation pond 300 may be configured to receive wastewater withreduced, environmentally acceptable levels of dissolved VOCs, or“treated water,” and to gradually introduce the treated water back intothe environment; e.g., by enabling the same to be evaporated into theatmosphere or, after the treated water has been further treated tocomply with governmental regulations, reintroduced to surface and groundwater.

In embodiments where the water treatment site 200 includes a clarifier294, sludge from the clarifier 294 may be transported back to thebioreactor 110.

A water treatment site 200 may comprise a system that is configured tobe closed and/or sealed from the OWS 220 to the bioreactor 110, or evenfrom the OWS 220 to the filter 290. Of course, the interiors of one ormore components of a system that is configured to be closed may beselectively accessed (e.g., to remove LNAPLs, to remove sludge, etc.),and the system may be configured to produce treated water and emissionsthat are less harmful than the VOCs that are emitted from wastewaterthat has not yet been fully treated.

With continued reference to FIGS. 4 and 5, various elements of a methodfor treating wastewater (in addition to those that should already beapparent from the foregoing description) are now described. Although thecontext for the ensuing description is a water treatment site 200, theportions of the disclosed method that relate to treatment of wastewaterin a bioreactor 110 may be employed in any system, regardless of whetheror not the bioreactor is configured in the manner shown in FIG. 2 or 3or any other way (e.g., as shown in FIG. 1, etc.) and regardless of theenvironment in which the bioreactor 110 is situated.

Initially, LNAPLs and, optionally, sludge may be separated from thewastewater. Separation may be achieved by any suitable means; use of theOWS 220 and/or the stilling basin 250 disclosed herein are merely acouple of examples. Separation may be effected by gravity,centrifugation or any other suitable technique.

In the context of a water treatment site 200, wastewater may be broughtto the water treatment site 200 by way of a tanker 205. Morespecifically, the tanker 205 may be positioned in proximity to an OWS220. The wastewater from the tanker 205 may be delivered into the OWS220 in any suitable manner. In some embodiments, delivery of thewastewater into the OWS 220 may be effected in a way that preventsintroduction of VOCs into the environment.

Prior to removing any LNAPLs or sludge from the OWS 220, the gas and/orvapor content of the OWS 220 may be monitored. In the event that harmfulgases are present, those gases may be drawn out of the OWS 220 before itis opened and incinerated or otherwise treated.

The wastewater may be allowed to remain in the OWS 220 for a sufficientperiod of time (e.g., a few hours, a few days, etc.) to enable LNAPLs(e.g., oil, gas, other hydrocarbons, etc.) that have mixed with thewastewater to separate from the wastewater. Once LNAPLs have separatedfrom the wastewater, they may be removed from the OWS 220 and stored ina storage tank 230, where they may be kept until a sufficient volume ofLNAPLs is collected to transport and sell (e.g., to a refinery, etc.).In addition to allowing LNAPLs to separate from the wastewater, sludge(e.g., DNAPLs, solids, etc.) may drop to the bottom of the OWS 220 whilethe wastewater sits therein. The solids, which may be referred to as“sludge,” may be periodically or occasionally collected from the OWS220.

In embodiments where the OWS 220 may be opened to remove LNAPLs orsludge, the gases and/or vapors within the OWS 220 may be monitoredprior to accessing its contents. As an example, levels of hydrogensulfide and other toxic materials or pollutants may be monitored priorto opening the OWS 220 and, if such materials are present, they may beremoved from the OWS 220 (e.g., drawn out of the OWS 220 andincinerated, etc.). As another example, oxygen levels within the OWS 220may be monitored.

Once the initial, or rough, separation of LNAPLs from the wastewater iscomplete, the wastewater may be transported to a flare 240, where gasesand/or vapors (e.g., undissolved VOCs, other potential pollutants, etc.)from the wastewater may be burned to form less harmful byproducts, whichmay then be released into the environment. In embodiments where thestilling basin 250 includes a flexible cover, a negative pressure thatdraws gases and/or vapors from the stilling basin 250 may continuouslydraw the flexible cover against the surface of the contents of thestilling basin 250. Optionally, a flexible cover of a stilling basin 250may be configured to accommodate gases and/or vapors even when the rateat which they are emitted from the wastewater exceeds the rate at whichthey are drawn from the stilling basin 250 (i.e., the cover mayaccommodate surges in gas and/or vapor production).

Following the initial, rough separation of LNAPLs and sludge from thewastewater, as well as any optional flaring, further separation ofLNAPLs and/or sludge from the wastewater may occur. In some embodiments,the wastewater may reside within a stilling basin 250 for a prolongedperiod of time. Any LNAPLs that collect at the surface of the wastewatermay be collected and placed in a storage tank 230. Any solids that dropto the bottom of the stilling basin 250 may remain there until thesolids, or sludge, are removed from the stilling basin 250. Therecovered sludge may be used for other purposes; for example, to formhardened roadway surfaces (e.g., at oil or gas exploration or productionfacilities, etc.).

Once sufficient separation has been achieved and LNAPLs have beenremoved from the wastewater, the wastewater may be examined to determinewhether or not it is suited for introduction into the bioreactor 110, orto determine how it should be introduced into the bioreactor 110. As anexample of such examination, the wastewater may be tested for thepresence of biocides, which are sometimes added to water used duringexploration and/or production. If undesirably high levels of biocidesare detected (e.g., sufficient levels to disturb the anaerobicmicroorganisms 126 of the bioreactor 110, etc.), the

As another example, the salt content or content of other TDSs in thewastewater may be determined. If the salt and/or TDS content of thewastewater is undesirably high (e.g., at or above a level that wouldhave a detrimental effect on the anaerobic microorganisms 126 whenintroduced into the bioreactor 110, etc.), the volume of wastewater thatis introduced into the bioreactor 110 may be limited (e.g., to an amountthat will not increase the salt or TDS content of the wastewater withinthe bioreactor 110 by more than a fixed amount (e.g., five percent, tenpercent, etc.) until wastewater with a lower salt or TDS content isavailable (e.g., until the levels of salt and/or other TDSs in thewastewater in the stilling basin 250 are diluted, etc.). Optionally, theintroduction of wastewater into the bioreactor 110 may be delayed untilthe TDS content of the wastewater in the stilling basin 250 reachesacceptable levels for introduction into the bioreactor 110 by dilutionfrom added wastewater, etc.). As another option, fresher water may beadded to wastewater with a high salt content or TDS content to dilutethe same. As yet another option, wastewater with a high content of saltor other TDSs may bypass the bioreactor 110. In some embodiments, theintroduction of wastewater with a low salt or TDS content into thebioreactor 110 may also be limited; for example, to volumes that willnot decrease the salt or TDS content of wastewater within the bioreactor110 by more than a fixed amount (e.g., five percent, ten percent, etc.).Moderation of the levels of salt and/or other TDSs within the bioreactormay minimize any detrimental effect on the microorganisms 126 within thebioreactor 110.

Once the wastewater has been introduced into the bioreactor 110, it mayremain there for a sufficient period of time to enable the anaerobicmicroorganisms 126 to metabolize VOCs and, optionally, other LNAPLs thatremain within the wastewater. In some embodiments, the wastewater may beperiodically mixed. Mixing may be effected by turbulence as wastewateris introduced into the bioreactor, by recirculating wastewater withinthe bioreactor, or otherwise, as known in the art.

All, or substantially all, gases and vapors that are present within thebioreactor 110 (e.g., over the surface of the wastewater therein andbeneath the cover 170, etc.) may be removed from the bioreactor 110(e.g., drawn therefrom, etc.), creating a substantially or totallyanaerobic environment within the vessel 112 of the bioreactor 110. Inembodiments where the cover 170 of the bioreactor 110 is flexible, thecover 170 may accommodate gases and/or vapors even when the rate atwhich they are emitted from the wastewater exceeds the rate at whichthey are drawn from the bioreactor 110 (i.e., the cover 170 mayaccommodate surges in gas and/or vapor production). The gases and/orvapors that are drawn from the bioreactor 110 may be transported to theflare 240, where they may be incinerated.

In some embodiments, including those where the vessel 112 of thebioreactor 110 includes a pond 150, portions of the wastewater may beperiodically or occasionally removed, meaning that some of thewastewater may be removed shortly after it has been introduced into thebioreactor 110. In any event, the anaerobic microorganisms 126 of thebioreactor 110 may remove sufficient levels of VOCs and other LNAPLsfrom the wastewater.

Once wastewater is recovered from the bioreactor 110, or in embodimentswhere wastewater bypasses the bioreactor 110, the wastewater may besubjected to further treatment. Examples of such treatment includefiltering to remove VOCs or other HAPs, reverse osmosis, clarification,placing the wastewater in one or a series of evaporation ponds, or anyother suitable process. The wastewater may be reintroduced into theenvironment, it may be used in exploration or production operations orit may be used for other acceptable purposes.

Any sludge that accompanies the treated water out of the bioreactor 110may be removed from the treated water and disposed of or returned to thebioreactor 110. In some embodiments, the sludge may be fortified withnutrients (e.g., ammonia, phosphoric acid, etc.) before it is returnedto the bioreactor 110. Alternatively, sludge from the bioreactor 110(which may have been removed with wastewater or separately from thewastewater) may be used to seed another bioreactor 110.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scopes of the inventions recited by anyof the appended claims, but merely as providing information pertinent tosome specific embodiments that may fall within the scopes of theappended claims. Features from different embodiments may be employed incombination. In addition, other embodiments of the invention may alsolie within the scopes of the appended claims. All additions to,deletions from and modifications of the disclosed subject matter thatfall within the scopes of the claims are to be embraced by the claims.

What is claimed:
 1. A method, comprising: containing wastewater andanaerobic microorganisms that digest hydrocarbons in the wastewater in avessel; covering the wastewater within the vessel with a cover; andapplying a negative pressure for drawing the cover against a surface ofthe wastewater within the vessel and for creating an anaerobicenvironment within the vessel.
 2. The method of claim 1, furthercomprising maintaining a periodic or continuous flow of liquids withinan interior of the vessel.
 3. The method of claim 1, further comprisingdetecting any leakage by the vessel and capturing any water as a resultof the leakage.
 4. The method of claim 1, further comprisingincinerating gases or vapors from the vessel to form byproducts to bereleased into the atmosphere.
 5. The method of claim 1, furthercomprising receiving the wastewater at the vessel from a stilling basinlocated at a higher elevation than an elevation of the vessel.
 6. Themethod of claim 1, further comprising removing sludge from treatedwastewater flowing out of the vessel.
 7. The method of claim 1, furthercomprising releasing treated wastewater from the vessel to one or moretreatment components comprising at least one of a filter, a reverseosmosis system, and an evaporation pond.
 8. A method for treatingwastewater from oil or gas exploration or production, comprising:collection untreated wastewater from an oil or gas exploration orproduction site; separating the untreated wastewater from hydrocarbonsand sludge in a stilling basin having a capacity of at least about10,000 barrels; mixing the untreated wastewater with treated wastewaterand with anaerobic microorganisms in the treated wastewater in abioreactor including a pond having a capacity of at least about 10,000barrels; treating the untreated wastewater with the anaerobicmicroorganisms to reduce a content of volatile organic compoundsdissolved in the untreated wastewater; and preventing the volatileorganic compounds dissolved in the untreated wastewater from escapinginto the atmosphere, wherein preventing the volatile organic compoundsdissolved in the untreated wastewater from escaping into the atmospherecomprises applying a negative pressure for drawing a flexible coveragainst a surface of the treated or untreated wastewater within thepond.